1. Field of the Invention
The present invention relates to an apparatus or classifier for sorting by size particles entrained in a gas-solid stream ejected from a feed nozzle by utilizing the Coanda effect.
2. Description of the Prior Art
There is a known method of and apparatus for sorting particles according to size by passing the feed mixture fluid containing the particles along a cyclonic arcuate surface through a jet stream from a feeding nozzle to impart a centrifugal action to the fluid. This system was reported by Mr. Okuda in the international Symposium Of Particle Technology held in Kyoto in September, 1981. This report discloses test results obtained by the system in which a high speed stream or jet stream of air entraining particles is bent at a small radius of curvature by utilizing the attachment of a stream to an adjacent surface (i.e. the Coanda effect) and imparting a relatively large amount of a centrifugal force to the particles entrained in the stream of the fluid so as to separate the particles by size. A similar method of classification is proposed in U.S. Pat. No. 4,153,541. These methods employ the effect derived from the action of the stream of fluid and the centrifugal force acting on the particles contained in the stream of the fluid, and they are suitable particularly for classification or separation of particles of a small size.
FIG. 13 of the accompanying drawings reillustrates a prior classifier in which a feed nozzle 3 ejects a jet stream of the gas entraining the particles tangentially with respect to an arcuate wall surface 2a of a cyclonic wall 2. The stream is attached to the adjacent wall 2a by the Coanda effect, and it is thus bent along the arcuate wall 2a for thereby forming a curved wall-attachment stream.
This apparatus has a drawback in that the velocity of the wall-attachment stream flowing close to the arcuate surface 2a is drastically reduced to zero, with the result that a centrifugal force acts on the particles entrained by the wall-attachment stream insufficiently through the length of the arcuate surface. The thus insufficient action of the centrifugal force on the particles fails to separate the particles sharply into oversized and undersized particles and thus allows the oversized particles to be included in the latter when the processed particles are collected. The prior apparatus achieves only a poor performance of classification.
It is therefore an object of the present invention to provide an apparatus for classifying particles, wherein the oversized particles are reliably separated from the undersized particles in the entraining stream flowing close to the cyclonic arcuate wall surface.